Blue Green stain- From coil?

I am pretty HVAC illiterate, so please forgive me. What is this green type stain that appears to have leaked out of the "coil" and has left a blue green stain. Also it has made a rust spot on the furnace. The picture is taken looking down on the furnace from the coil. Thanks for any help.

Corroding copper (the coil's tubing is likely copper) produces a compound that color. You should check the drain pipe and the drain pan under the coil and make sure it does drain properly. It looks like the drain is plugged, overflowed, and that's the reason for the staining on top of the furnace. Long term, that could rust out things inside, decreasing the life of the thing. Also, if the drain line does not have a trap in it, one should be added. I have one similar to this...it makes it easy to clean things out with the supplied (on some versions) brush.

Attached Files:

Attached Files:

As pointed out by JAD, the plug right above the pipe is a secondary drain...which should NOT be plugged. It is meant to act as a tell-tale if the primary drain is clogged, to prevent the drain pan overflow which apparently you are experiencing.

FWIW, there are two sets of two drain plug holes in the case to allow for either vertical or horizontal airflow. Since yours (should) be configured for upflow, I think they're using the wrong drain plugs, and the coil may not have been installed properly for your application. This would make the pan inoperable if it isn't installed properly as well.

FWIW, there are two sets of two drain plug holes in the case to allow for either vertical or horizontal airflow. Since yours (should) be configured for upflow, I think they're using the wrong drain plugs, and the coil may not have been installed properly for your application. This would make the pan inoperable if it isn't installed properly as well.

Click to expand...

I think in his photo, "UP" is on the LEFT, so I interpret that he is using the right set of holes, just should open up the secondary port.

As pointed out by JAD, the plug right above the pipe is a secondary drain...which should NOT be plugged. It is meant to act as a tell-tale if the primary drain is clogged, to prevent the drain pan overflow which apparently you are experiencing.

I think in his photo, "UP" is on the LEFT, so I interpret that he is using the right set of holes, just should open up the secondary port.

Click to expand...

Sorry for the confusing photo. Hope this helps.
PICTURE TAKEN LOOKING DOWN ON THE DRAIN PIPE FROM ABOVE. What do you mean by open up the secondary port? I have never done PVC work, so maybe hamstrung here?

Can I just go the where the pvc enters the floor drain and try to suck it out with shop vac etc?

As mentioned your drain pan is overflowing and that is what is shown on top of your furnace. Since a furnace is a "blow-through" coil a trap is only needed if local codes call for it but it is a good idea to keep vapors from entering the unit during its off cycle. Please retake the picture "Facing" the bottom of the coil as it sits on top of your furnace so the drain "primary and secondary" ports can be seen better.

In actual orientation, you see two fittings side by side ( one should be just slightly higher than the other. Not more than 1/2"). The lower one is the main drain, and in your photo the other one has a square head plug, but should instead have a drain line connected. The second set of fittings.....both plugged, is used if the coil is operated horizontal instead of vertical. They should remain plugged.

Unless you pull a panel off and look, you can't know if it's leaking (probably overflowing) and could be dripping down on sensitive parts.

If it's leaking from the fitting, the only way to resolve that is to cut the pipe off, screw in a new fitting, and rebuild it from there. But, if the drip pan in there is clogged up, or the fitting is clogged, you need to clean that out first. If I were to rebuilt it, I might put a T instead of that elbow with a plug so I could take that off and run a brush or a piece of coat hanger in there to clean things out.

In your photo, it looks to me like the pipe is connected to the slightly higher fitting....the secondary. That is very wrong, and the slightest clog will cause overflow of the pan, which is what you seem to have.